今天fedora9的yum突然失灵，已解决，跟大家分享

今天进入FC9，发现yum不能用了，跟这位兄弟一样的问题：http://www.linuxdiyf.com/viewarticle.php?id=91615
贴出来分享一下过程，希望对有类似问题的朋友有所帮助。
因为也不知道是什么原因，所以做了各种尝试，过程比较乱，不知道哪些有用哪些没用，希望大家指正，共同进步：
1.我先是在图形界面改了下设置：面板上－系统－>管理->Add/Remove Software->system->software sources,然后在所有选项上打钩，但是发现它们自己会刷新回原状，于是放弃。
2.然后我在图形界面又点了系统升级，报出错误：cannot find a valid baseurl for repo:core，百度了一下，找到办法说是要修改/etc/yum.conf,如下：
[main]
cachedir=/var/cache/yum
keepcache=0
debuglevel=2
logfile=/var/log/yum.log
pkgpolicy=newest
distroverpkg=redhat-release
tolerant=1
exactarch=1
obsoletes=1
# Don't check keys for localinstall
gpgcheck=0
plugins=1
metadata_expire=1800
# Changed this because some mirrors go down and then
# re-trying takes forever.
timeout=7


# PUT YOUR REPOS HERE OR IN separate files named file.repo
# in /etc/yum.repos.d
我看了一下原来的，还是有不同，于是照着改了。
3.然后又说要升级yum，那里给的是旧版，我干脆把光盘上的拿来用－－replacepkgs重装了一道。个人感觉是心理安慰而已。
4.然后重试yum update,错误变了，起作用了，一阵窃喜。。。
报错如下：
[root@localhost ~]# yum update
Loaded plugins: fastestmirror, refresh-packagekit
Repository livna is listed more than once in the configuration
Repository livna-debuginfo is listed more than once in the configuration
Repository livna-source is listed more than once in the configuration
Loading mirror speeds from cached hostfile
* atrpms: dl.atrpms.net
* kde-redhat-stable-all: mirror.unl.edu
* livna-development: rpm.livna.org
* kde-redhat-stable: mirror.unl.edu
* livna-development-debuginfo: rpm.livna.org
* livna: ftp3.tsinghua.edu.cn
* fedora: 203.200.188.111
* rawhide-source: ftp.yz.yamagata-u.ac.jp
* fedora-debuginfo: opensource.nchc.org.tw
* updates-testing-debuginfo: ftp.kaist.ac.kr
Could not retrieve mirrorlist http://fedora.redhat.com/download/mirrors/fedora-core-9 error was
[Errno 14] HTTP Error 404: Not Found
Error: Cannot find a valid baseurl for repo: core
接下来就简单了，进入/etc/yum.repos.d/fedora-updates.repo,把http://fedora.redhat.com/download/mirrors/fedora-core-9搜出来，把那段配置删了，就是两个空白行中间那些全删，记得养成备份的好习惯哦～～
接着yum update,成功！但就是感觉网速好像有点变慢